The present invention relates generally to processes for removing impurities from heavy fuel, and more particularly, to methods and systems that remove corrosive metal compound impurities from heavy fuel with the use of a stationary adsorption column.
Hydrocarbon oils represent a type of crude oil (petroleum) found throughout the world, that consists of a complex mixture of hydrocarbons (mostly alkanes). In most cases, the hydrocarbon oils (e.g., the heavy oils) are processed and refined into other useful petroleum products, such as diesel fuel, gasoline, heating oil, kerosene, and liquefied petroleum gas. Such other petroleum products are then used for various industrial purposes, such as for combustion fuel in a gas turbine engine.
It is well known in the art that hydrocarbon oils, like other organic compositions derived prehistorically from nature, contain at least small amounts of contaminating compounds containing metals, sulfur, and other elements and compounds, such as nitrogen. For example, crude oil from regions such as Saudi Arabia often contains relatively high levels of many of these contaminants. Such contaminants are detrimental to the direct use of the hydrocarbon oils as a fuel (e.g., use of the oil with minimal processing), and may be detrimental to the processing of the oil to produce other commercially valuable products.
As an illustration, when used with gas turbine engines, impurities in the fuel cause corrosion to the turbine blades and/or other components. More specifically, vanadium compounds may form hard deposits on turbine blades which may promote corrosion. In addition to material degradation and processing problems in refineries, the presence of contaminants, such as sulfur, may also result in environmental and/or regulatory problems. For such reasons, the operating efficiency of gas turbine engines operating with such fuel oil types may be adversely affected.
Metal contaminants in heavy oil, such as nickel and vanadium, are usually present in the form of one or more organo-metallic compounds, such as various porphyrinic compounds. The metallic compounds can be present in the form of non-porphyrin metal species as well, e.g., as metal salts. Moreover, other elements which may be present in crude oil include potassium, lead, sodium, and iron.
A number of techniques have been used in an attempt to remove impurities from oil, and/or in an attempt to minimize their harmful effects. In general processes, distillation techniques commonly used in oil refining remove some of the contaminants, as various oil fractions are boiled off in traditional distillation columns. However, such distillation techniques may be very energy-intensive.
Catalytic hydrodesulfurization techniques have been used to remove sulfur from crude products. However, vanadium and nickel impurities that are also present in the oil tend to adhere to the catalysts and thereby block the active site, thus diminishing the efficiency of the desulfurization reactions. Further, this process may be expensive to operate.
Magnesium compounds are sometimes used to address the problems of metal contamination. For example, magnesium is capable of forming relatively low-melting alloys with contaminant metals such as vanadium. Such low-melting compounds can be removed more easily (e.g., by washing) from the surface of turbine blades, as compared to the harder, higher-melting contaminants themselves.
While the use of the magnesium compounds may be suitable in some situations, their use may be limited in some situations. For example, the compounds may form excessively hard deposits if the underlying part (for example, a gas turbine component) is exposed to higher temperatures, e.g., greater than about 2,000° F. (1093° C.). In these situations, deposits remain adhered to the metal surfaces. Thus, the use of such gas turbine components may be limited unnecessarily to lower operating temperatures. Moreover, combustion of the lower-melting magnesium-vanadium alloys can result in the generation of significant amounts of ash, which may form a residue on an underlying substrate, e.g., the turbine blades. Such deposits can also adversely affect the gas flow path over the turbine blades. Furthermore, removing such deposits may require shutting down the turbine.
In view of these concerns, new techniques for reducing the level of metallic or non-metallic impurities in heavy oils are desirable. The improved processes should be capable of substantially reducing the level of at least some of the impurities in the heavy oils in a cost-effective and energy-conservative manner. Moreover, these techniques should not adversely affect other treatment processes to which the heavy oil is subjected.